There are known mobile radio communication systems such as WCDMA (Wideband Code Division Multiple Access), LTE (Long Term Evolution), LTE-A (LTE-Advanced, and WiMAX (Worldwide Interoperability for Microwave Access) by 3GPP (Third Generation Partnership Project). These mobile radio communication systems can increase the communication area by a cellular configuration in which the area covered by a base station (a base station device, a transmission station, a transmission device, eNodeB) or a transmission station conforming to the base station is arranged as a plurality of cells.
The aforementioned mobile radio communication system can realize a more efficient data transmission by adaptively controlling the modulation and coding scheme (MCS), the number of spatial multiplex (layers, rank), precoding weight (precoding matrix) and the like according to the communication path status between a base station and a terminal device. NPL 1 set forth below discloses a method of such control.
FIG. 17 represents an example of a SU (Single User)-MIMO (Multiple Input Multiple Output, spatial multiplex transmission) in a transmission mode using the dual layer beam forming scheme of LTE. A base station 1701 transmits two transmission data addressed to a terminal device 1702, i.e. transmission data 1703 and transmission data 1704, using two ports (logic ports) that are spatial-multiplex for a terminal device 1702, i.e. a port 7 and a port 8. A reference signal of port 7 and a reference signal of port 8 are multiplied by spread codes orthogonal to each other. Accordingly, terminal device 1702 can readily have the reference signal of port 7 and the reference signal of port 8 separated.
FIG. 18 represents an example of downlink multiple user (MU)-MIMO in a transmission mode using a dual layer beam forming scheme of LTE. A base station 1801 uses port 7 and port 8 that are two spatial-multiplexed ports, as disclosed in NPL 2 set forth below, to transmit transmission data 1804 addressed to a terminal device 1802 and transmission data 1805 addressed to a terminal device 1803 at the same time and using the same frequency towards terminal devices 1802 and 1803. The reference signal of port 7 and the reference signal of port 8 are multiplied by spread codes orthogonal to each other. The terminal device is configured to identify in which port its own addressed transmission data is included by using downlink control information. Terminal device 1802 and terminal device 1803 can readily separate the reference signal of port 7 and the reference signal of port 8. Furthermore, terminal device 1802 and terminal device 1803 can extract the transmission data by demodulating the received data using a reference signal corresponding to its own addressed port.
FIG. 19 represents another example of downlink MU-MIMO transmission in a transmission mode using a dual layer beam forming scheme of LTE. A base station 1901 uses port 7 that is one of the two ports that are spatial-multiplexed for a terminal device 1902 and a terminal device 1903 to transmit transmission data 1904 addressed to terminal device 1902 and transmission data 1905 addressed to terminal device 1903 at the same time and using the same frequency. Although base station 1901 sends transmission data 1904 and transmission data 1905 through the same port 7, the directivity of the signals for sending respective transmission data can be set independently. Specifically, base station 1901 sends transmission data 1904 in a first directivity 1906 and transmission data 1905 in a second directivity 1907. The reference signal for terminal device 1902 and the reference signal for terminal device 1903 are multiplied by scrambling codes quasi-orthogonal to each other. Base station 1901 notifies terminal device 1902 and terminal device 1903 about information indicating respective scrambling codes through downlink control information. Accordingly, terminal device 1902 and terminal device 1903 can separate the reference signal of its own port 7 using the difference in directivity and difference in the scrambling code.
FIG. 20 represents a part of downlink control information in LTE. A code word (CW) is a group of transmission data. The control information includes, in addition to the 16 bits of information related to CW1 and CW2 that are code words, a 1-bit scrambling code identification (SCID) indicating the type of scrambling code, as disclosed in NPL 3 set forth below. For each CW, a MCS (modulation and coding scheme) indicator (MCSI) indicating the MCS is represented in 5 bits, a new data indicator (NDI) indicating whether the transmission is the initial delivery or not is represented in 1 bit, and the redundancy version (RV) indicating the puncturing pattern is represented in 2 bits.
In LTE, the CW addressed to four terminal devices at most can be transmitted by MU-MIMO relative to the two ports shown in FIG. 18 by multiplying the two scrambling codes according to the 1-bit SCID shown in FIG. 20 by each port, as shown in FIG. 19.
In LTE-A that is an extended version of LTE, there is proposed increasing the highest multiplex value of SU-MIMO to 8 while keeping the backward compatibility to LTE, as described in NPL 4 set forth below.